The mayor of London, Boris Johnson, poses at the rear of a full-scale model of the capital's new double decker bus. Photograph: Reuters

Boris Johnson, the mayor of London, unveiled a red, life-size, mock-up of the New Bus for London this morning, describing it as a vehicle in progress that would combine "a sense of nostalgia" for the much-loved Routemasters with cutting-edge design and technology.

The first working buses would probably be on the capital's streets by the end of next year or early 2012, Johnson said.

The bus, which has yet to be formally named, is being developed for Transport for London by Wrightbus, of Ballymena, Northern Ireland, in partnership with the designer Thomas Heatherwick.

Posing for photographs at the Transport Museum depot in Acton, west London, on the mock-up's rear open platform – a direct throwback to the Routemaster – Johnson praised the environmental advantages of the new bus, saying it would emit 40% less carbon dioxide than a regular diesel double decker and 15% less than the current generation of hybrid technology buses, which make up part of London's fleet. Fuel consumption would fall in line with emissions.

The bus has long been politically controversial, with critics condemning it as a vanity project and damning its £10m development costs. During the 2008 London mayoral election campaign, Johnson was dogged by questions about the cost of the scheme and had difficulties answering them.

However, he claimed vindication this morning, insisting that the bus was a groundbreaking innovation that would set new standards for urban bus travel and bring in orders from around the world. The old Routemasters were decommissioned under his predecessor, Ken Livingstone.

Important features of the bus will be two internal staircases and three sets of doors, facilitating rapid exit and entrance of passengers, one of the advantages of the articulated "bendy buses" which Johnson has been phasing out since his election.

Johnson confirmed that the new bus would also have a conductor on board some of the time.

Peter Hendy, Transport for London commissioner, said that staff would be trained and recruited for the task rather than being, for example, police community support officers, as Johnson once suggested they might be. Hendy stressed their role would include "doing some of the things people expect of a person in uniform", such as assisting passengers on and off the rear open platform and ensuring people have swiped their Oyster cards.

Hendy and Johnson explained that the rear platform could be kept open during journeys with a second staff member present, enabling passengers to "hop on and hop off" between stops. However, with only a driver present the rear platform would be closed off between stops with an automatic door, operated by the driver.

The interior of the bus has also been "inspired" by the Routemaster, with the seat fabrics acknowledging past designs. The evolving design will now be presented to transport stakeholder groups, such as disabled people, for fine-tuning before its completion and launch.